In a technical field of a drive device, which has an electric motor and a motor housing, it is known to fix the motor housing to an installation subject. Here, the installation subject is defined as a subject, to which the motor housing is installed. For example, JP2014-180103A discloses an electric power steering apparatus, in which a motor housing is fixed to a gear housing, which serves as the installation subject, with use of screw bolts.
However, like in the case of JP2014-180103A where the fixing members, such as the screw bolts, are used to fix the motor housing to the installation subject, flange portions, through which the fixing members are respectively inserted, may need to be provided in the motor housing. This may result in an increase in an outer diameter of the motor housing. The increased outer diameter of the motor housing may become a barrier against size reduction of the drive device.